Conductively heated pitot static tube



Dec. 29, 1942. v. E. CARBONARA CONDUCTIVELY HEATED PITOT STATIC TUBE Filed Aug. 2, 1938 111114 wllull/ \NVENTGR \/%TUR EEHRBDNHRH BY v Patented Dec. 29, 1942 T FFECE Victor E. fiarbonara, Rockviile Centra'N. 15., as-

signor, by mesne assignments, to Square D Company, Detroit, Mich, a corporation of Michigan Application August 2, 1938, Serial No. 222,663

3 Claims.

This invention relates to airplane speed responsive instruments of the Pitot-static tube type and relates particularly to a Pitot-static tube having de-icing means for preventing the accumulation of ice in or upon the tube structure.

In the prior art of the construction of Pitotstatic tubes, difiiculty has been encountered in keeping the tubes free from ice during bad flying weather and particularly in keeping them free from ice and in operating condition while flying in snow or in conditions which tend to cause them to collect ice or sleet.

It has been customary with prior Pitot-static tubes to provide a streamlined shell having therein a Pitot tube or dynamic pressure member, opening at the forward tip of the shell, and slots or perforations in the side of the shell to insure a correct static pressure value, corresponding to the actual air pressure of the height at which the plane is flying, within the shell. Both the dynamic pressure tube and the static pressure shell interior are connected by suitable tubular duct lines to the indicator member which is a pressure sensitive instrument adapted to respond to the pressure differential between the dynamic pressure conveyed to the instrument from the Pitot tube and the static pressure existing within the shell, and to indicate the pressure differential in terms of air speed.

Previously constructed Pitot-static tubes have,

however, suffered from thedisadvantage that under bad atmospheric conditions or in the presence of spray it has not always been possible to keep the Pitot-static tube free of obstruction and in operating order. During clear, good, flying weather the readings of the air speed indicator are of interest, but not vital to the navigation of the plane. However, in bad flying weather when the pilot is flying on instruments, and

under the necessity of estimating the distance r flown by a dead reckoning computed from the indicated air speed andelapsed time, it is of importance that his air speed indicator be wholly reliable, but it is under bad atmospheric conditions that the air speed indicator and Pitot tube combination is in most danger of failure. Such failure is usually due to obstruction of the Pitot tube or of the static shell by frost, ice or water from the spray, or from the fog, rain or snow through which the pilot may at the moment he In the copending applications of Paul Kollsman, Serial Nos. 135,858 filed April 9, 1937, and Serial No. 195,465 filed March 12, 1938, now Patent 2,221,547 granted Nov. 12, 1940, there is disclosed a Pitot-static tube construction in which there is incorporated a controlled heater member adapted to provide sufficient heat to prevent obstruction of the dynamic pressure tube by ice or snow which may tend to accumulate thereon, or therein.

The present invention provides a Pitot tube in which particularly efficient and efiective means are incorporated to insure freedom of the entire Pitot tube structure from ice or snow under any operating conditions. It consists of a streamlined shell which includes a Water trap of the type shown in the 'copending application of Paul Kollsman, Serial No. 205,765, filed May 3, 1938, now Patent 2,204,367, as desired, and may be adapted for mounting upon a long tubular strut, or on a short socket, as desired. Within the shell there is provided means for delivering heat energy to a plurality of critical points upon the shell,

which when kept warm enough to remain free from ice prevent the formation of ice anywhere upon the shell. The means for providing the heat energy may consist of one or more local heating means and associated therewith, there may be heat conducting means such as metal fins leading from the heating means to the interior of the shell at a position back of the static pressure slots where the application of heat will result in the most efficient de-icing of the shell exterior.

It has been customary in airplane construction to provide de-icing devices in the form of overshoes or inflatable rubber covers on structures which tend to collect ice during flying in bad weather, and if the Pitot-static tube structure is mounted upon the end of a strut attached to the fuselage it is satisfactory to cover the strut with the rubber over-shoes" which by inflation with air can be caused to break loose and dislodge any ice which may collect thereon. This construction cannot, however, be extended down to the Pitot tube shell proper because of the interference of eddy currents produced thereby in the static pressure slots and on occasion in the dynamic pressure duct; for which reason it is necessary that other de-icing means be provided for the Pitot-static tube and shell.

One troublesome point for ice collection is the forward tip end of the Pitot-static tube structure. The formation of ice at this point, however, is well prevented by the structures disclosed in the above mentioned copending applications of Paul Kollsman, but it is found that under the more severeweather conditions merely preventing the formation of ice in and upon the tip of the structure is not suilicient but that ice may tend to collect upon the shank of the structure (particularly if there are irregularities, bends or curva tures in the structure) at the point of turbulence produced thereby, even though the turbulence produced is small in amount; and ice once started to form at such points increases the turbulence conditions and the speed of ice formation, until the static pressure slots are covered and in some instances the whole structure covered with ice, thereby disabling all of the instruments which obtain their air pressures from the Pitot-static tube device, such as the air speed indicator and in many instances the altimeters.

Thus an object of the invention is to deliver heat energy to a Pitot tube shell at a part where ice is most likely to form.

Another object of the invention is to deliver heat to a plurality of locations upon the shell of a Pitot tube structure.

Still another object of the invention is to apply heat directly from a local heating means to one portion of a Pitot tube shell and to appl heat by guided conduction from the same heating means to another part of the shell.

Yet another object of the invention is to prevent th formation of ice upon the Pitot-statlc tube at points of curvature, bending or enlargement of the shell structure to prevent the collection of ice at points behind the static pres- I sure slots.

A further object of the invention is to apply heat to a variety of places upon a Pitot tube shell by a plurality of means including the direct application of heat from a heating means and the simultaneous application of heat from the same means or a separate heating means to a plurality of points by simultaneous direct delivery and by guided conduction to another position.

Other objects and structural details will be apparent from the following description when read in connection with the accompanying drawing. The claims are directed to the illustrative embodiments for illustration rather than limitation..

Fig. 1 is a side view in vertical section of an embodiment including a water trap and means for the heating thereof;

Fig. 2 is a front view partly in section of the embodiment of Fig. 1;

Fig. 3 is a side view in vertical section of a portion of another embodiment showing a different arrangement of the heating means; and

Fig. 4 is a rear view of the embodiments of Figs. 1 and 3.

Referring to the drawing, particularly Figs. 1 and 2, a simple embodiment of part of the invention may consist of a streamlined shell member I attached to a mounting plug member 2 and having therein a dynamic pressure duct 3. A local heating means 4 shown as a resistance coil is provided and supplied with controlled electric energy through the conductors 8. The dynamic pressure duct 3 is connected through chamber I! to a tubular duct line 1 leading outwardly to the indicating instrument (not shown). In addition static pressure slots 8 are provided in the shell I to establish within the shell a static pressure corresponding to the elevation at which the plane is flying and the pressure within the shell I is conveyed to the indicating instruments through a second tubular duct line 9.

The local heating means 4 is attached to the shell I by any convenient means which may preferably be by electro-deposition of the shell I upon its sealed metallic casing or capsule II. as disclosed in my copending application Serial No. 124,839, filed February 9, 1937.

In the operation of Pitot-static tubes it has been found that as long as the temperature remains substantially above the freezing point, ice does not tend to form either upon or within the tube structure, but that during flying in bad weather such as in mist or super-cooled fog or in snow, ice or other forms of congealed water may tend to collect upon the exterior of the shell I, and within the dynamic tube 3. One point upon which such ice first tends to collect is the forward tip of the Pitot-static tube structure since it is the point where the most active disturbance of air occurs and where the strongest precipitating forces occur. The collection of ice upon the tip of the structure is, however, well prevented by the heater 4 corresponding to the structures of the prior art. However, elimination of i e from the tip alone is not sufilcient since the strut upon which the Pitot-static tube is mounted also produces air disturbances; and the collection of ice on the bend and at the junction between the Pltot-static tube structure and the strut also creates sufflcient turbulence and disturbance to cause the rapid precipitation of ice (it being understood that the precipitation occurs under sleeting conditions or when there is supercooled moisture in the air). Under these conditions the ice tends to collect on and around the base of the shell structure until a suflicient quantity has accumulated to extend well up the shank of the structure towards the forward tip and to cover the static pressure slots. Under particularly bad icing conditions, the amount of ice collected may be greater than can be kept down by the tip heater previously used and the whole structure may becom coated with ice. When this stage is reached both the air speed meter and the altimeter, if they are connected to the static pressure lead as is usually the case, are disabled and may fall of functioning entirely.

It is found that by placing a heater such as the local heating means 4 close to the forward end of the tube structure particularly with its casing 40 in direct contact enough heat can be liberated at the forward end of the tube to keep the tube surface at the end above the freezing point, and thereby under mild conditions prevent the attachment thereto of precipitated ice.

During flying in snow relatively little of the snow tends to collect upon the exterior of the tube, but substantial quantities of snow are blown through the opening II into the tube 3 and may be blown into the tube in sufficient quantity to pack in the tube and obstruct it to the point of preventing functioning. The heating means 4 supplies suflicient heat to the tube 3 to melt from it any snow which may enter and' allow the melted snow to drain outward through the front end.

For heavy duty service, especially for service which requires the Pitot static tube structure to be at a higher point than the indicator, the embodiment of the invention shown in Figs. 1 and 2 is particularly advantageous because of the inclusion of a trap member to prevent the passage of water into the instrument connecting tube lines.

In addition to heating means 4, there is provided a second heating means I5 of like construction and positioned within the shell I rearwardly of static pressure slots 8. A partition I6 is also provided closing off the protuberant portion 11 or the shell to form a fluid trap. The

dynamic pressure duct 3 leads from the pressure port ll through the partition i6 into the space within the trap l1 and a tube I8 entering the trap I! and terminating near the top of the trap chamber is provided and connected to the instrument line 1. Static pressure slots 8 in the shell insure a normal pressure corresponding to the altitude of flight within the shell I, and the second instrument line 9 is connected to the static pressure space within the shell] by way of an auxiliary trap member 19. A heat conducting fin member 2| is also provided leading from the heating means l to the forwardsurface of the trap portion H. The trap portion l! of the shell produces a substantial amount of air disturbance even though it is well and efficiently streamlined and accordingly the leading edge of the protuberance housing the trap is a part which is particularly likely to collect ice when the conditions favor the deposition of ice upon the structure. Furthermore when ice starts to form upon the leading edge of the trap it forms in considerable quantities and quickly builds up to the point of covering the static pressure slots 8 as above described. It is for the purpose of preventing this accumulation of ice that the heating means l5 and fin 2| are included in the structure.

During flying under sleeting conditions, the position on the shell at which ice first tends to collect isthe center of the forward edge of the trap member I! and ice tends to build up quite rapidly upon the trap I1 and extend downward over the rest of the shell until the. ports 8 are either covered or eddy currents produced in the neighborhood thereof by the ice which cause false pressures within the shell I. The formation of ice upon the trap member I! is prevented by heat conducted thereto from the heating means 15 and accordingly, with no ice forming upon the forward leading surface of the trap l1, there is no opportunity for an ice deposit to grow and any additional heat supplied to the trap l1 spreads to other parts of the shell and prevents the deposition of ice on the rear portion of the shell structure as a whole, at the same time that the heating means 4 prevents the deposition of ice on the forward portion of the shell as previously described. Furthermore, the heating means 4 prevents the plugging of the dynamic duct with snow and the heating means l5 and fin 2i prevent freezing in the trap I! of any water which may be blown in through the duct 3, thereby permitting such water todrain backward and out through the drain port 22.

The embodiment of Figs. 1 and'2 is shown with the second heating means l5 located within the shell I below the trap H. For particularly severe service, it is in some instances advantageous to have a portion of the heating means l5 within the trap 11 as shown in Fig. 3, thereby shortening the fin member 23 and insuring a more effective and rapid delivery of heat to the critical part of the shell. Otherwise the construction is closely similar to that of the embodiment of Figure 1 and similar reference characters indicate similar parts.

The embodiments of the device as shown in the drawing and above described thus present a Pitot-static tube structure in which there is provision for the application of heat both to the dynamic pressure duct and to a plurality of parts on the shell and particularly to the parts of the shell where ice first tends to form during sleeting conditions; the invention .particularly presents a combination of one or more heating means with heat conducting members extending cooperatively to the shell of the tube at positions behind the static slots and positions where ice tends to form first, for the efiicient delivery of heat to such parts of the shell to prevent the formation of ice thereon or therein and thereby keep the entire shell and tube structure free from ice and therefore free from obstructions and in complete operating condition.

While there are above disclosed but a limited number of embodiments of the device of the invention it is possible to provide still other embodiments thereof without departing from the inventive concept herein disclosed and it is therefore desired that only such limitations be imposed upon the appended claims as are stated therein.-

What I claim and desire to protect by United States Letters Patent is:

l. A Pitot-static tube structure comprising, in combination, a shell having a hollow protuberance thereon, said shell having a dynamic pressure opening at the front end and a static open-- ing at the side thereof; a partition in said shell separating an interior portion of said protuberance from the remainder of the space in said shell; a dynamic pressure duct within said shell connecting said dynamic opening with the hollow of said protuberance above said partition; a continuation duct leading from a point near the top interior of said protuberance downwardly and out of said shell; a second duct leading outward from the interior of said shell; a heating element positioned internally near the forward end of said shell adjacent said dynamic pressure duct; a second heating element positioned nearer to said protuberance; and a heat conveying member arranged to conduct heat from said second heating element to an outer wall of said protuberance.

2. A Pitot-static tube including a shell having a main portion and a water trap portion forming a protruding part of said shell; an electric heating element enclosed within a metallic capsule and positioned partly within the water trap portion and partly within the main portion of said shell; and a metallic heat conducting member metallically connecting said capsule with a forwardly positioned wall of said trap.

3. A Pitot-static tube which comprises a shell having a hollow protuberance thereon, said shell having a dynamic pressure opening at the front end and a static opening at the side thereof; a partition in said shell separating an interior portion of said protuberance from the remainder of the space in said shell; a dynamic pressure duct within said shell connecting said dynamic opening with the hollow of said protuberance above said partition; a continuation duct leading from a point near the top interior of said protuberance downwardly and out of said shell; a second duct leading outward from the interior of said shell; heating means including an electrical coil within a metallic capsule positioned internally near the forward end of said shell adjacent said dynamic pressure duct; a second heating means including an electrical coil within a. metallic capsule positioned nearer the said protuberance; and a heat conducting member connecting said last mentioned capsule to the front wall of said protuberance to conduct heat from said second heating means to said front wall of the protuberance.

VICTOR E. CARBONARA. 

